IP Addressing Fundamentals

Chapter 4. Variable-Length Subnet Masks

The preceding chapter examined the powerful innovation known as subnetting in its original form: Fixed-Length Subnet Masking (FLSM). At its introduction, FLSM was called simply subnetting. By any name, it was a revolutionary and necessary evolution of the IP address architecture that enabled a tremendous reduction in the waste of IP addresses. With the benefit of hindsight, we can see that FLSM was but a half step in the right direction. Its single greatest benefit was that it validated the concept of borrowing bits from the host field of an IP address to create locally significant subnetwork identification addresses. But the simplifying assumption of permitting just one subnet mask for all subnets created ...